The sudden infant death syndrome (SIDS) is the cmmonest cause of death in the age period 1 month to 1 year. Two hypotheses as to its etiology are being explored (a) segmental intimal proliferative lesions in the myocardial small arteries and arterioles reduce perfusion to the myocardial conduction fibers and thereby predispose to arrhythmias and death (b) chronic alveolar hypoxia is a common pathway of death in SIDS. Both of these hypotheses can be tested by searching for certain anatomic abnormalities in brain, heart, lungs and several abdominal organs. Quantitative, histlogic methods and gross quantitative methods are to be used to search for the appropriate abnormalities.